A typical wireless communication system may comprise a plurality of wireless communications devices transmitting and receiving messages with each other. These messages are typically arranged in formatted groups of data called frames. Each frame may comprise a header and a payload. The header may be used by the wireless communication system for routing the data within the frame to the desired recipient, whereas the payload represents the data generated by a user to be transmitted.
An advantageous wireless communication system is IEEE 802.16a-e (WiMAX), for example. The WiMAX wireless communication system typically includes a wireless base station and a plurality of wireless communications devices communicating therewith. Moreover, the WIMAX wireless communication system is typically based upon a frame structure that is defined by a plurality of sub-carriers at different frequencies and a plurality of symbols at different transmission times.
The wireless base station logically allocates data for transmission to each of the wireless communications devices in the system on to the sub-carriers, i.e. subchannelization. Typically, a wireless communications device is allocated a plurality of sub-carriers that are adjacent in the frequency domain, each group of sub-carriers including at least one pilot sub-carrier (pilot tone) to define a sub-carrier group (subchannel). The pilot sub-carriers typically are used for network entry, more particularly, not for network entry entirely but for the ranging process, which is part of network entry in WiMAX. Ranging is the generic process by which WiMAX tailors its wireless properties for best performance under the current conditions for transmitter/receiver synchronization, and ranging, for example. In other words, the pilot sub-carriers may be important for efficient operation of the WiMAX wireless communication system.
As wireless communication systems have become more prevalent, a robust security infrastructure has become desirable. Several approaches to developing such a security infrastructure have been disclosed. For example, the messages transmitted in the wireless communication system may be encrypted using an encryption algorithm, for example, Wired Equivalent Privacy (WEP), Advanced Encryption Standard (AES), and Data Encryption Standard (DES).
Although typical encryption of messages in the wireless communication system may provide for security of the payload data of a frame, there may be several security drawbacks to the typical encrypted wireless communication system. One such drawback may be the lack of security for the actual transmitted frames. In other words, a system infiltrator, for example, an intentional interfering device, may listen to the communications of the system and sniff transmitted frames. In particular, in WiMAX wireless communication systems, the intentional interfering device may determine the corresponding frequencies of the pilot sub-carriers. Once known, the intentional interfering device may concentrate narrowband interference at those frequencies and render the pilot sub-carriers indiscernible to the wireless communications devices of the system, thereby possibly reducing the operational efficiency of the WiMAX communication system.
Particularly, the pilot sub-carriers in the WiMAX 802.16d standard are static. Hence, a WiMAX 802.16d wireless communication system may be susceptible to intentional interference. Although the WiMAX 802.11e standard does provide modification features for the pilot sub-carrier, the changes in pilot sub-carrier location (in the frequency domain) may be made during system set up. In other words, the re-allocation of pilot sub-carriers may cause the wireless communication system downtime. This may translate into increased latency in communications, which results in lower data rate as experienced by a user and performance decline in the user's applications. Moreover, this approach may: cause the wireless communication system to be reconfigured, use customized bandwidth provisioning and resource allocation, and render the wireless communication system non-interoperable or difficult to integrate with other systems.
An approach to sub-carrier allocation is disclosed in U.S. Patent Publication No. 2005/0180354 to Cho et al. This approach allocates sub-carriers based upon the type of data throughput requested by the user, i.e. dynamic or static. Another approach is disclosed in U.S. Patent Publication No. 2007/0263743 to Lee et al. This approach includes partitioning orthogonal frequency-division multiple access (OFDMA) sub-carrier groups and symbols based upon a basic pilot pattern generated by a specific reference, allocating the sub-carrier group based upon the partitioned sub-carrier groups and the symbols, hopping the sub-carrier groups according to a hopping pattern, allocating data, and allocating the pilot per sub-carrier group based on the basic pilot pattern from the hopped data.